1. Field of the Invention
The present invention relates to liquid crystal display (LCD) devices, and more particularly to a substrate bonding device facilitating the fabrication of LCD devices formed via liquid crystal dispensing methods and a method for fabricating LCD devices using the same.
2. Background of the Related Art
With the expansion of the information society, a need has arisen for displays capable of producing high quality images in thin, lightweight packages and that consume little power. To meet such needs, research has produced a variety of flat panel display devices, including liquid crystal displays (LCD), plasma displays (PDP), electro luminescent displays (ELD), and vacuum fluorescent displays (VFD). Some of these display technologies have already been applied in information displays.
Of the various types of flat panel display devices, LCD devices are very widely used. In fact, in portable devices, such as notebook PC computers, LCD technology has already replaced cathode ray tubes (CRT) as the display of choice. Moreover, even in desktop PCs and in TV monitors, LCDs devices are becoming more common.
Despite various technical developments in LCD technology, however, research in enhancing the picture quality of LCD devices has been lacking compared to research in other features and advantages of LCD devices. Therefore, to increase the use of LCD devices as displays in various fields of application, LCD devices capable of expressing high quality images (e.g., images having a high resolution and a high luminance) with large-sized screens, while still maintaining a light weight, minimal dimensions, and low power consumption must be developed.
LCDs generally include an LCD panel for displaying pictures and a driving part for providing driving signals to the LCD panel. Typically, LCD panels include first and second glass substrates bonded to each other while being spaced apart by a cell gap, wherein a layer of liquid crystal material is injected into the cell gap.
The first glass substrate (i.e., thin film transistor (TFT) array substrate), supports a plurality of gate lines spaced apart from each other at a fixed interval and extending along a first direction; a plurality of data lines spaced apart from each other at a fixed interval and extending along a second direction, substantially perpendicular to the first direction, wherein pixel regions are defined by crossings of the gate and data lines; a plurality of pixel electrodes arranged in a matrix pattern within respective ones of the pixel regions; and a plurality of thin film transistors (TFTs) capable of transmitting signals from the data lines to corresponding ones of the pixel electrodes in response to signals applied to respective ones of the gate lines.
The second glass substrate (i.e., color filter substrate) supports a black matrix layer for preventing light leakage in areas outside the pixel regions; a color filter layer (R,G,B) for selectively transmitting light having predetermined wavelengths; and a common electrode for displaying pictures. Common electrodes of In-Plane Switching (IPS) mode LCD devices, however, are formed on the first substrate.
Uniformity of the cell gap is maintained by spacers arranged between the first and second glass substrates, bonded together by a seal pattern. The seal pattern includes a liquid crystal injection opening allowing liquid crystal material to be injected into the cell gap by a capillary phenomenon. Upon injecting liquid crystal material into the cell gap through the liquid crystal injection opening, the layer of liquid crystal material is thus formed.
Fabricating LCD devices using the aforementioned related art liquid crystal injection method, however, is disadvantageous because the productivity of such liquid crystal injection methods is poor. More specifically, after LCD panels are formed by a cutting process, liquid crystal material is injected into the cell gap by dipping the liquid crystal injection opening of each LCD panel into a reservoir of liquid crystal material while pressure in the cell gap is maintained in a vacuum state. Moreover, as the size of the LCD panel increases, the risk of defects within the LCD panel increases due to imperfect filling characteristics of the liquid crystal material. Further, the liquid crystal injection methods are often complicated, time consuming, and require many liquid crystal injection devices that occupy excessive amounts of space.
In light of the aforementioned problems associated with liquid crystal injection methods, fabricating LCD devices by dispensing liquid crystal material have been the subject of recent research. More specifically, Japanese Patent Application Nos. H11-089612 and H11-172903 can be understood to disclose a method of dispensing liquid crystal material wherein, after liquid crystal material is dispensed and sealant material is coated onto one of the first and second substrates, the other of the first and second substrates is positioned on the one of the first and second substrates and the two substrates are bonded together under a vacuum.
Generally, liquid crystal material dispensing methods are advantageous over liquid crystal material injection methods because they reduce the number of fabrication steps required to fabricate LCD panels (e.g., formation of the liquid crystal injection hole, injection of the liquid crystal material, sealing of the liquid crystal injection hole, etc., are omitted), thereby simplifying fabrication of LCD panels.
FIGS. 1 and 2 illustrate a related art substrate bonding device used in fabricating LCD panels formed with dispensed liquid crystal material.
Referring to FIGS. 1 and 2, the related art LCD device substrate bonding device is provided with a frame 10, an upper stage 21, a lower stage 22, a sealant dispensing part (not shown), a liquid crystal material dispensing part 30, an upper chamber unit 31, a lower chamber unit 32, chamber moving means, and stage moving means.
The sealant dispensing part (not shown) and liquid crystal dispensing part 30 are typically provided at a side portion of the frame 10. Moreover, the upper and lower chamber units 31 and 32, respectively, can be joined to each other to bond substrates of an LCD panel.
The chamber moving means generally includes a driving motor 40 for moving the lower chamber unit 32 laterally to predetermined positions where the substrates are to be bonded (S2) and where the sealant material is to be coated and the liquid crystal material is to be dispensed (S1). The stage moving means includes a driving motor 50 for raising and lowering the upper stage 21 to predetermined positions.
A method for fabricating an LCD panel using the related art substrate bonding device will now be described in greater detail.
A first substrate 51 is positioned on the lower stage 22 of the lower chamber unit 32 and the chamber moving means 40 moves the lower chamber unit 32 under the upper chamber unit 31 such that the lower stage 22 is beneath the upper stage 21. Next, the driving motor 50 of the stage moving means lowers the upper stage 21 to a predetermined position such that the first substrate 51 is secured to the lowered upper stage 21. Subsequently, the upper stage 21, to which the first substrate 51 is secured, is raised to a predetermined position. The chamber moving means 40 then moves the lower chamber unit 32 to a position where a second substrate 52 is loaded on the lower stage 22. Subsequently, the chamber moving means 40 moves the lower chamber unit 32 to a first predetermined position S1 (as shown in FIG. 1). At the first predetermined position S1, sealant material coating and liquid crystal material dispensing processes are applied to the second substrate 52 using the sealant dispensing part (not shown) and the liquid crystal dispensing part 30, respectively. After the coating the sealant material and dispensing the liquid crystal material, the chamber moving means 40 moves the lower chamber unit 32 to a second predetermined position S2 (as shown in FIG. 2) where the first and second substrates 51 and 52, respectively, can be bonded together. Next, the upper and lower chamber units 31 and 32, respectively, are joined to each other such that the upper and lower stages 21 and 22, respectively, are arranged within an enclosed space. A vacuum is then created within the enclosed space using an evacuating means (not shown). After the vacuum is created, the stage moving means 50 lowers the upper stage 21 such that the first substrate 51, secured to the upper stage 21, contacts the second substrate 52 on the lower stage 22. The upper stage 21 is lowered until the two substrates become bonded, thereby completing the fabrication of the LCD panel.
Use of the aforementioned related art substrate LCD device substrate bonding device is disadvantageous, however, because the overall size of the aforementioned related art substrate bonding device is excessively large, especially when designed to fabricate large-sized LCD panels. The excessively large overall size of the related substrate bonding device creates problems when designing LCD device fabrication processes because an adequate amount of space must be provided to install the related art substrate bonding device while preserving the space in which other apparatuses of other processes are located.
Further, while the related art bonding device applies sealant and liquid crystal material to substrates supporting thin film transistors and color filter layers and bonds the two substrates together, the related art bonding device may increases the overall amount of time required to fabricate one LCD panel. More specifically, because liquid crystal material is dispensed, sealant material is coated, and substrates are bonded all using the same apparatus, substrates transported from preceding processes must stand idle until the processes performed by the related art substrate bonding device are complete. Moreover, the overall productivity of the LCD fabrication process is reduced since the related art substrate bonding device cannot process material transported thereto while other fabrication processes are in progress.
Still further, an imperfect seal can be formed between the joined upper and lower chamber units 31 and 32, respectively. As a result, air may leak from the external environment into the enclosed space defined by the upper and lower chamber units and the substrates may become damaged during bonding, thereby creating a defective bond.
Moreover, a substantially high degree of alignment is required to position the lower chamber unit 32 and successfully bond the two substrates. Such alignment can be extremely difficult and complicated and unduly lengthen the entire process of fabricating the LCD panel. Accordingly, the many positions the lower chamber 32 is required to move to (e.g., the first position S1 for dispensing the liquid crystal and coating the sealant material onto the second substrate 52, the second position S2 for bonding the two substrates, etc.) prevent the substrates from being properly aligned for a successful bonding.